Right after around 78% of level completion you might find a small texture under a wall saying:

R.I.P - "Stumpy" Thing 227 201-2011

It seems to be some sort of inside joke as thing 227 is in fact a health bonus and not a "STUMPY" which are the peaked brown things. Curious enough one of the pits near where this health bonus shall spawn (at the beginning of the map) does not hurt the player... maybe the map creator is telling us something...

Once you use the blue switch, get back outside with the nearby teleporter and then head into the new opening leading westward. There are two satyr switches near the next door. Use the one on the right to find a megasphere in one of the nearby alcoves. (sector 677)

After making the jump to the blue key, return to the previous cavern and go back to the switch used to reach the blue key cavern. There will be some steps leading up to a soul sphere and a backpack. (sector 690)

Head into the lava at the start, then head all the way to the right to the soul sphere. Quickly run back west and enter the opening to the north before it closes to get health bonuses and a backpack. (sector 691)